Portable telephones are equipped with, in addition to a standard telephone function and an email exchanging function, a camera function for photographing a subject, a browsing function for browsing websites, and a TV function for watching TV programs. Portable telephones have been used by people in a wide range of generations not only as a means for carrying out communications, but also as a multifunctional personalized terminal that serves as a digital camera, a personal computer, a TV and so forth. Under such circumstances, portable telephone manufactures are emulously adding new functions to their own products to make them unique.
Functions that have been newly added to recent portable telephones include a pedometer and a GPS function. For example, Japanese Laid-open Patent Publication No. 2000-227341 describes a technique for virtually displaying a travel path on a display screen according to the number of steps measured by the pedometer. When a portable telephone that is almost always carried by a user is equipped with a pedometer in this way, the user can readily know the total number of his/her steps for one day, enhancing the user's motivation for doing exercise. Also, when a portable telephone is equipped with a GPS function, it is possible to recognize the current position of a user carrying the portable telephone, enabling the portable telephone to serve as a means for preventing crimes as well as a navigation device for leading the user to destinations.
Meanwhile, since users usually carry their portable telephones when traveling, there has been devised a route recording function for recording travel paths made on a trip by using the portable telephone. Japanese Laid-open Patent Publication No. 10-170300 describes a technique for estimating the current position by calculating a travel distance between the initial position and the current position using a value obtained by a pedometer, thereby displaying the estimated current position determined based on the travel distance on a map. According to the technique described in Japanese Laid-open Patent Publication No. 10-170300, since the estimated current positions are sequentially recorded, the user can review the entire routes after retuning from the trip.
However, the above-described method for calculating the current position based on the travel distance has such a problem that an error between the predicted current position and the actual current position is large, making it impossible to obtain precise traveling paths made on the trip. In order to acquire the current position precisely, it is preferable to use a GPS function instead of using a pedometer provided in the portable telephone. However, a GPS function requires a large amount of power consumption. Therefore, when the GPS function is provided in a portable terminal with a battery of low capacity and the GPS function is kept active all the time, the battery quickly goes dead, making the portable terminal inoperable. For this reason, it is necessary to control turning on and off of the GPS function in order to suppress power consumption.
FIG. 1 is a flowchart that illustrates a flow of processes for recording a travel path using a GPS function.
When a user selects a route recording function using an operation member, the GPS function of a portable telephone is activated, information representing the current position of the user is acquired, and then the GPS function is stopped (step S1 of FIG. 1). Subsequently, the information representing the current position is recorded in a memory of the portable telephone (step S2 of FIG. 1).
After a lapse of predetermined time (e. g., 30 seconds) (step S3 of FIG. 1), the GPS function is activated again and the information representing the current position of the user is acquired (step S1 of FIG. 1), and subsequently the information representing the current position is recorded in the memory (step S2 of FIG. 1).
This sequence of processes is periodically repeated until the user gives an order to halt the operation of the route recording function with an operation member.
When an order to display a travel path on a display screen is given by the user, there appears a map that indicates the travel path linking the positions represented by the position information recorded in the memory. By checking the travel path on the map displayed on the display screen, the user can reliably and readily review the routes made on a trip.
Here, according to the method illustrated in FIG. 1, the portable terminal keeps recording the information representing the current position even when the user is eating or sleeping, until the halt of the route recording function is ordered. Therefore, when the user is on a trip including stay for nights, if the GPS function is kept active in order to record all the paths made on the trip, the power of the battery is quickly used up. Besides this, a memory with a large capacity for recording a great amount of information is required. However, there is such a concern that it is difficult to provide the inside of the portable telephone with space for accommodating a large battery or a large memory with sufficient recording capacity, because downsizing of portable telephones has been rapidly promoted.